Chronic Obstructive Pulmonary Disease (COPD) is characterized by the progressive development of irreversible airflow limitation. COPD consists of chronic obstructive bronchitis, with obstruction of small airways, and emphysema, with enlargement of air spaces and destruction of lung parenchyma, loss of lung elasticity, and closure of small airways. In COPD patients, there were increased numbers of neutrophils, cytotoxic T lymphocytes and macrophages in bronchioalveolar lavage (BAL) airways and lung parenchyma. The presence of these inflammatory cells is correlated well with severity of airway obstruction and alveolar wall destruction. It has been shown that neutrophil elastase; cathepsin G and proteinase 3 can produce emphysema and mucus hypersecretion in lab animals. Granzymes A & B are the neutral serine proteases that are expressed exclusively in the granules of activated cytotoxic T lymphocytes. In COPD the protease-antiprotease balance appears to be tipped in favor of increased proteolysis due to increase in polymorphonuclear neutrophil (PMN)-derived proteases, cathepsins and matrix metalloproteases (MMPs). Therefore, a drug that inhibits all or most of the relevant proteases mentioned above is expected to be effective in the treatment of COPD.
Dipeptidyl Peptidase-1 (DPP-1, cathepsin C) is a member of the lysosomal papain-type cysteine protease family that also includes cathepsin B, K, H, L, O, and S. DPP-1 (MW 200 kd) is composed of a dimer of disulfide-linked heavy and light chains, both from a single protein precursor. DPP-1 mRNA is highly expressed in tissues such as lung, spleen, kidney and liver; in inflammatory cells such as PMN, cytotoxic T lymphocytes, alveolar macrophages and mast cells. The biological function of DPP-1 is to convert inactive proenzymes into active enzyme by removing a dipeptide from N-terminal. The proenzymes that are activated by DPP-1 are PMN-derived proteases, granzymes A & B, chymase and tryptase. Since these enzymes play an important pathological role in COPD, inhibition of DDP-1 by small molecules would be a rational therapeutic intervention for COPD. Additional therapeutic indications for a DPP-1 inhibitor are asthma, rhinitis, and rheumatoid arthritis.
There remains a need for inhibitors of DPP-1 for the treatment of DPP-1 mediated disorders and conditions, including but not limited to rheumatoid arthritis, asthma, chronic obstructive pulmonary disease, sepsis, irritable bowel disease, cystic fibrosis, and abdominal aortic aneurism.